The invention relates to a flip chip package of monolithic microwave integrated circuit (MMIC), and more particularly, to a flip chip package of MMIC that has optimum heat-dissipative characteristic, and that can reduce the effects of parasitic inductance and parasitic capacitance, for the application in micro-wave, millimeter-wave and radio-frequency.
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FIG. 1 is a structural disposition of a microwave integrated circuit package according to a prior art. As shown in FIG. 1, the microwave integrated circuit package structure disclosed in patent No. 69,402 of Taiwan, Republic of China includes a grounded potential metal surface 112, an IC chip bonding part 113, a slot-type via hole signal line 115 penetrating through the substrate, a coplanar waveguide input/output port (I/O port) 121, and a plurality of circular via holes connecting the top and bottom metal surfaces of the substrate. The microwave integrated circuit package provides a grounded potential metal surface to perform signal transmission between each of the I/O ports and IC circuit. As far as the disposition of the metal surface on the substrate""s top surface is concerned, the material employed for the metal surface is any ones that can be performed wire bonding and are chemically stable. And the metal surface is fabricated by making use of thick film or thin film or a common IC board""s etching methods, and its attenuation is smaller than that of a micro-strip since it employs coplanar waveguide.
FIG. 2 is a cross-sectional view of a microwave integrated circuit package according to another prior art. The prior art shown in FIG. 2 is a xe2x80x9csmall outline integrated circuit (SOIC) packagexe2x80x9d which is the most popular IC package technology nowadays. As shown in FIG. 2, the steps for forming the SOIC package is described as follows. First of all, a chip 281 is adhered to the paddle 221 of the lead frame 282 by the surface mounting method. Afterwards, the wires 283 are bonded, and adhesive material 284 is applied to fix the package in position. The package is finally formed by mold injection with encapsulant 285 to protect against the intrusion of the moisture and the dust that might affect the electrical characteristic in order to improve the package reliability.
FIG. 3(a) is a cross-sectional view of a microwave integrated circuit package according to one other prior art. The microwave integrated circuit package is disclosed in patent No. 93,511 of Taiwan, Republic of China. As shown in FIG. 3(a), the microwave integrated circuit package includes an IC chip 363 and a substrate 361. Wires 331, 332 are employed to connect the I/O ports 341, 342 of the IC to the I/O ports 321, 322 of the substrate""s top surface. They are further connected to the I/O ports 323, 324 of the substrate""s bottom surface through the via holes 315, 316 at the left and right edges of the substrate. Afterwards, underfill material 390 is employed to cover the IC chip 363 and bonding wires 331, 332 to fix the IC chip in position. Finally, the package is formed on the top of the underfill material 390 by mold injection with encapsulant 391.
FIG. 3(b) is an isometric top view of a microwave integrated circuit package according to the one other prior art shown in FIG. 3(a). As shown in FIG. 3(b), the IC chip 416 is flipped over to have the surface, having signal and ground terminals, facing downward. In the meantime, metal strip 411, 412 are widen such that the input signal terminal of the IC chip 416 can contact the metal strip 411, the output signal terminal can contact the metal strip 412, and the all the grounded terminals can contact the metal strip 415. Moreover, the portion covered by the IC chip 416 is performed etching to prevent the surface of the IC chip 416 from being short-circuited.
Most of the above-mentioned package technology makes use of bonding wires to connect the IC chip to the I/O ports of the substrate. Since the bonding wires of this kind of chip-and-wire IC package will cause significant parasitic inductance effect and parasitic capacitance effect in the frequency range of micro-wave and milli-meter wave, the chip-and-wire IC package will affect the electrical characteristic in the high frequency range and deteriorate the reliability of the electronic devices. Moreover, among the MMIC packages, the manufacturing cost of this kind of chip-and-wire is rather high nowadays, and its mass production is not feasible. Further, the size of the MMIC made by chip-and-wire is rather large that does not meet the trend of compact design in package.
Currently, in respect of the frequency range of micro-wave and milli-wave application, although the micro-wave integrated circuit (MIC) formed by employing bare chip and wire bonding is widely used, the fabrication process is time consuming and the cost of manpower is very high, thereby, the price of the MIC package remains very high. Besides, since the bonding wires currently employed by the microwave chip package results in parasitic inductance effect and parasitic capacitance effect, the electrical performance is deteriorated, consequently, the application of the wire bonding in milli-wave package is not even feasible.
On the other hand, a comparison of the invention with the prior art shown in FIG. 3(b) is made as follows. Since the invention employs metal strips to connect the IC chip to the substrate, and since the area of the substrate is only slightly greater than that of the IC chip, the size of the device after finishing the packaging process is rather small. Therefore, the MMIC package of the invention is in accordance with the trend of the compact design of the package. In addition, since the IC chip is electrically connected to the substrate through the metal strip instead of being directly contacted the substrate, the short circuit phenomenon on the surface of the IC chip can be avoided, thereby, the yield of the package of the electronic device is improved
In the light of the above-mentioned disadvantages, and in order to resolve the problems on the package used in radio frequency (RF), microwave, and milli-wave devices, an object of the invention is to have a package that can make use of the common surface-mounted technology (SMT) to undertake mass production so as to lower the production cost. The above-mentioned problems are summarized as follows:
1. The undesired impedance matching and the self-resonant problems resulted from the parasitic capacitance and parasitic inductance generated by the bonding wires.
2. The inability problem to undertake automation on the production of the chip-and-wire package.
3. The inertly heat-dissipative problem of the chip of gallium arsenide (GaAs) commonly used by the RF, microwave, and milli-wave.
4. The inability to have a compact package since the size of the package becomes large after the packaging process.
To attain the object of resolving these problems, the invention provides a flip chip package of monolithic microwave integrated circuit (MMIC). The MMIC package of the invention includes a substrate, having an top surface and a bottom surface, and each of the surfaces is divided respectively into a periphery area and a central area; an integrated circuit chip (IC chip), having a first surface and a second surface, and each of the surfaces being divided respectively into a periphery area and a central area, and the MMIC package being made by flipping the IC chip to have its first surface covering on the top surface of the substrate, and the central area of the first surface having one or several active devices; a plurality of metal strips, positioned on the IC chip""s first surface and disposed in the periphery area of the IC chip""s first surface, and these metal strips being electrically connected to the active devices on the first surface of the IC chip; a plurality of solder bumps, implanted respectively on and being electrically connected to the first surface""s metal strips of the plurality of IC chips; a plurality of metal strips of the substrate ""s top surface, disposed in the periphery area of the substrate""s top surface, and these metal strips being electrically connected to the plurality of solder bumps; a plurality of metal strips of the substrate""s bottom surface, disposed in the periphery area of the substrate""s bottom surface; a plurality of via holes, penetrating through the substrate and being electrically connected to the plurality of metal strips of the substrate""s top surface and to the plurality of metal strips of the substrate""s bottom surface respectively; and an underfill, filling the solder bumps and the plurality of the metal strips which are connected to the solder bumps and are positioned on the IC chip""s first surface, also filling all the chinks around the top surface""s metal strips of the substrate, and covering the whole IC chip up to a height that is slightly higher than the thickness of the MMIC chip. A penetration hole is provided in the central areas of the top and bottom surfaces of the substrate for those high power packages that require optimum heat-dissipative effect. Moreover, the material removed by penetrating the penetration hole is replaced by filling a heat-dissipative material with relatively low dielectric constant and relatively low dielectric loss.